Safety connection on electric lifts



Oct. 2, 1934. o, G T-HNGER 1,975,420

SAFETY CONNECTION ON ELECTRIC LIFTS filed July 31, 1930 Fig. Fly. 2 W

Patented Oct. 2, 1934 UNITED STATES PATENT OFFICE Oskar Giittinger, Lucer to Schindler & Cie,

ne, Switzerland, assignor Lucerne, Switzerland Application July 31, 1930, Serial No. 472,178

In Germany 3 Claims.

The present invention relates to improvements in safety control arrangements for electric elevators and the like, and has for its object to provide an arrangement which, in case of the accidental grounding of the control circuit, the operation of the elevator is prevented until the electric connections are restored to proper condition.

In the accompanying drawing wherein two approved embodiments of the invention are illustrated:

Figures 1 and 2 are diagrammatic views of elevator installations illustrating the invention applied thereto.

Referring to the drawing in detail and more particularly to Fig. 1, an elevator and the operating electric motor therefor are shown diagrammatically, the current for the operation of the installation being supplied over the threephase main lines EST. The safety switches associated with the elevator are indicated at 2, 3, 4, 5 and 6 and the control switch located in the elevator is indicated at 7. The reversing switch 8 is operated from the control switch 7 in the elevator. The control circuit is supplied with current by a transformer 11 connected across the main lines RS, one terminal of the secondary winding of the transformer being connected over the fuse 9 with the safety switches 2 to 6 and the other end of said winding being connected with the operating coil windings of the reversing switch 8. The conductor leading from the secondary winding of the transformer is connected at 10 with a conductor which is suitably grounded at E in the elevator installation.

If an accidental grounding of the control circuit occurs at the safety switch 6, for instance, as indicated by the arrow at this point, the control circuit is closed from one side of the transformer 11 through the fuse 9, safety switches 2 to 6 to the accidental ground connection at this point, and thence over the conductor connected at point 10 to the opposite side of the transformer winding without, however, affecting the coils of the reversing switch 8. Owing to the low resistance offered by the short grounded circuit, the value of the current flowing therethrough increases and the fuse 9 is thus blown out, thereby opening the control circuit and interrupting the operation of the elevator until the trouble is corrected.

In the modification of the invention illustrated in Fig. 2, the ground conductor 10 instead of being connected with the end of the secondary winding of the transformer 11, is connected to a central tapping thereof. The opposite end of the August 6, 1929 ground conductor 10 is connected with a suitable ground connection E of the elevator installation.

The conductors from one side of the secondary winding of the transformer to the coils of the reversing switch 8 and on the other side to the safety switches 26 lead over excessive current responsive means 9 for opening the circuit and, as will be understood, these current responsive means may take the form of a fuse.

Under normal working conditions the full value of the current induced in the secondary winding flows over the control circuit when the control switch '7 is operated and the coils of the reversing switch 8 are so constructed as to operate only when energized by the full value of this current.

However, when the control circuit is accidentally grounded, as for instance, at the point indicated in Fig. 2, adjacent the safety switch 6, the current induced in one-half of the secondary winding of the transformer is short circuited between the ground connection E and the ground at the switch 6, and consequently only the current induced in one-half of the secondary winding flows through the coils of the reversing switch 8 and this current, as will be understood, is insufiicient to properly energize the reversing switch coils. Accordingly the operation of the elevator is interrupted until the damage is repaired.

The division of the secondary winding into two parts and the connection of the central point thereof with the ground presents two advantages, first, accidental short circuits are less frequent because at any point of the control circuit to the ground only half of the tension of the transformer can occur, and second, electrical contact with current conducting control parts is less dangerous without reducing the control tension, the ground connection for the secondary winding of the transformer being provided during the actual manufacture of the apparatus thereby avoiding possibility of error in the judgment of the builder in making the ground connection for the arrangement such as shown in Fig. 1.

What I claim is:

1. A safety control system for elevator installations and the like comprising a transformer having a secondary coil, a control current circuit including the secondary winding of the transformer, for supplying control current to the said circuit, control devices in said circuit including electromagnetic operating coils for operating reversing means, safety switches, overload current responsive means for opening the said circuit, a ground connection to approximately the center of the said secondary coil, the said overload current responsive means being interposed between the respective ends of the said secondary coil and the remaining control devices, whereby any control device will upon becoming grounded permit the current to thus follow a short circuit path back to the said secondary winding by way of the first named ground connection, said short circuit path being or such low resistance that the value of the current rises to a sufficiently large value to cause the operation of the said current overload responsive means to efiect opening of the first named circuit.

2. A control system for electric elevator installations and the like comprising a transformer having a secondary winding, a control current circuit including the secondary winding of the transformer, a reversing switch including coils, the coils of the reversing switch being directly connected to one side of said winding, a fuse, safety switches connected over said fuse to the other side of said winding, and a ground connection between the secondary winding of the transformer and the coils of the reversing switch.

3. A control system for electric elevator installations and the like comprising a transformer having a secondary winding, 2. control current circuit'including the secondary winding of said transformer, a reversing switch including coils, a fuse, the coils of the reversing switch being connected on one side over said fuse to said windand a ground connection with the center of the secondary winding of the transformer.

OSKAR Gi'iTrINGER. 

